Prevention of deposition of pitch in papermaking



.pulps whether bleached or unbleached or nited States 3,081,219 PREVENTION F DEPUSiTION 0F PiTCH IN PAPERMAKING Thomas I. Drennen, Lafayette Hill, and Louis E. Keiley, Wyncote, Pa., assignors to Rohm 8r Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Feb. 10, 1960, Ser. No. 7,743

7 Claims. (Cl. 162-72) The present invention relates to the control of pitch in the making of paper from sulfite pulps. This application is a continuation-in-part of our copending application Serial No. 788,523, filed January 23, 1959, now abandoned.

The pitch in the fibers of wood pulps is associated with naturally occurring lignin dispersing agents. However, cooking and mechanical agitation which occur during the pulping by the sulfite process liberates the pitch but the natural dispersing agents liberated with the pitch are inadequate to keep the pitch from depositing, as a result of the mechanical work on the fibers, on the equipment employed in beating, hydrating, refining, bleaching, and even on the wire used for forming the sheet. Because of the tendency of the pitch to agglomerate within the pulp suspension or deposit on the surfaces of the wire or other equipment and then to break free in the form of particles of considerable size, the pitch frequently causes the formation of spots or holes in the sheet formed or may adhere to the wire or press rolls or drier rolls and cause tearing of the sheet. This results in occasional tearing of the sheet during formation or in the production of sheets with numerous imperfections. Among other consequences involved are the expense of cleaning the machinery frequently either with solvents or steam, and the loss of production during cleaning and during re-lacing opera tions caused by breakdown of the sheet.

- Various systems have been employed heretofore for controlling the pitch in the making of paper from sulfite from groundwood pulps. One way of controlling pitch heretofore employed is the introduction of diatomaceous earth, bentonite, or the like for the purpose of introducing finelydivided particles which adhere to the pitch and reduce the tackiness of its surface. Other expedients involve the addition of dispersing agents or sequestering agents. Polyphosphates such as sodium hexa-meta-phosphate have been employed. They have appreciable value when the pulp treated has a pH of about 3.5 to 4.5; but when the pulp is nearer the neutral state such as at a pH from 5.5 to 7, the beneficial effect is slight. Various dispersing agents have been employed such as the sodium salt of sulionated formaldehydc/ naphthalene condensates, but these agents have decreased etiects at neutral pH values. They also are precipitated by cationic materials, such as alum and cationic urea-formaldehyde-polyarnine wetstrength resins, so that pitch control suitors and the wetstrength efficiency of such resins is reduced when the latter materials are added to the pulp, as in the beating stage. There have also been suggestions to employ a mixture of an organic solvent for the pitch in conjunction with a dispersing agent, but these procedures involve the additional expenses of the organic solvent and of compounding the emulsifier therewith.

In accordance with the present invention, it has been fdiSCOVGlGd that highly eifective pitch control of suliite pulps over a wide range oi pH from both neutral to acid conditions can be obtained by the introduction of relatively small amounts of a polymeric N-vinyl lactam. The polymers contain from 80 to 100% of the N-vinyl lactam and up to 20% by weight of a neutral comonomer such as. a C -C3 ester of acrylic acid or methacrylic acid.

3,081,219 Patented Mar. 12, 1963 ice The polymers with which the present invention is con-' cerned contain N-vinyl lactam units of the general formula group, such as, for example, l-vinyl-Z-pyrrolidone, which in more recent terminology is called 'l-vinyl-Z-pyrrolidinone, 1-vinyl-5-methyl-2-pyrrolidinone, l-vinyl-Z-piperidone, N-vinyl-e-caprolactam, and the like. Depending upon the extent of polymerization, they have molecular weights ranging from 500 to 200,000. Viscosity measurements are used as an indication of the average molecular weight of the polymers which are characterized by a chain of carbon atoms to which the lactam rings are attached through their nitrogen atoms:

The viscosity coefficient K, which is fully described in Modern Plastics, 23, No. 3, 157-61, 212, 214, 216, 218 (19-45), is calculated as follows:

where C is the concentration in gram per cc. of polymer solution and 1 is the ratio of the viscosity of the solution to that of pure solvent. The K values are reported as 1000 times the calculated viscosity coefiicient in order to avoid the use of decimals. For the purpose of the present invention, there may be used those polymers having a K value of 10 to 100, preferably of 30 to 100 because of their viscosity at lower concentrations.

The preferred lactams are the N-vinyl-2-pyr-rolidinones having the general formula Iii- Ka o Br-HC 0:0

N H=CBIz wherein R represents hydrogen or methyl group and R represents either hydrogen, methyl, or ethyl.

As illustrative examples of such N-vinylpyrrolidinones the following may be mentioned:

' quired is in the range from about 0.005 to 0.2%

*cluding introduction prior gestion.

sesame Examples of the esters of acrylic acid or methacrylic acid, which acidshave the generic formula of the alkanols having from 1 to 18 carbon atoms including methanol, n-propanol, isopropanol, nbutanol, hexanol, Z-ethylhexanol, n-octanol, lauryl alcohol, and stearyl alcohol. The cyclohexanol, benzyl alcohol, bornyl alcohol, and isobornyl alcohol esters may also be employed.

The proportion of N-vinyl lactam polymer that is reby weight, based on the weight of fiber in the pulp. A larger amount of the polymer may be used, such as up to 0.5% by weight Or more, based on polymers of thepresent invention are so eiiicient in their pitch-controlling action that less than 0.2% of the polymer the weight of fiber. However,

onfiber is generally entirely adequate and the preferred range is from about 0.02 to 0.1% polymer on-fiber. The

mon papermakers alumn. the polymeric N-vinyl lactams of the present invention is the fact that they are unaffected by either anions or cations so that loss of pitch control is not-caused by the use of alum in rosin sizing or of cationic wet-strength resins.

The polymeric N-vinyl lactam may be introduced into the pulp at any stage The polymeric -vinyl lactam may be introduced into the pulp at any stage of the papermaking process, such as during beating, in the stock-chest, or even in the headbox of the papermaking machine. It is preferred to add the polymeric N-vinyl lactam early in the pulping or papermaking stage before the pitch initially dispersed by the lignin agent liberated from the pulp performed on the pulp during the papermaking operations. The best results are thereby obtained since the N-vinyl lactam polymer is not required to redisperse 1 coagulated pitch but only to stabilize the initially dispersed state. However, addition pitch in its in the later stages is effective in controlling the pitch but a larger amount of the polymer may be required to obtain a given When the addition of the polymer is made after digestion, headbox, the consistency of the pulp to which it is added may be from 0.01% to 6% fiber weight.

Generally pitch deposition is not a problem in 'a kraft pulp, but the polymers of the present invention can be applied to kraft pulps in those rare instances where pitch control is desirable.

In the following examples which are illustrative of the invention, the parts and percentages are by weight unless otherwise specifically indicated. The test method used high frequency, a having dimensions rizontally 2.5 cm.

a ing plate, only 0.5 part of vsistency).

4 8927, made by the A. H. Thomas Company. The apparatus used in the test also includes a collar (of l cm..outside diameter and 10 cm. length) on a rotating agitator shaft disposed so that the collar is at the surface of the pulp. The total weight of pitch collected on the vibrating plate and the collar is weighed to indicate the extent of deposition or control thereof. The time of agitation and vibration for the test is thirty minutes, and the temperatnre of the pulp during such agitation and vibration is 25 C. In all examples, the percentage of the N-vinyl lactam polymer is based on the weight of fiber (dry) in the pulp to which the polymer is added.

Example I 0.35% by weight of a copolymer of of N-vinyl- 2-pyrrolidinone with 5% of ethyl acrylate is introduced into an unbleached sulfite pulp having a pH of 6.5% and a 3.5% pulp consistency. On testing with the vibratpitch is deposited per 1,000 parts of pulp (3.5 consistency), whereas several batches of the untreated pulp under similar conditions deposited from 18 to 25 parts per 1,000 parts of pulp (3.5% con- The employment or" 0.35% of the sodium salt of asulfonated formaldehy'de/naphthalene condensate results in a deposit under similar conditions of 16.0 parts per 1,000 parts of pulp (3.5 consistency).

Example 2 A deposit of 0.9 part of pitch per 1,000 parts of pulp (3.5% consistency) occurs when 0.7% (on the weight of pulp) of a copolymer of 95% of N-vinyl-Z-pyrrolidinone with 5% of lauryl methacrylate is employed for pitch control and tested as in Example 1. The employment of 0.7% by weight on the pulp of the sodium salt of a sulfonatcd formaldehyde/naphthalene condensate results in adeposit of 7 parts of pitch per 1,000 parts of pulp (3.5 consistency) at a pH of 6.5.

Example 3 When the test of Example 1 is repeated but-substituting 0.7% of a copolymer of 95% of N-vinyl-2-pyrrolidinone and 5% of isobornyl methacrylate, only 0.7 part of pitch per 1,000 parts of pulp (3.5% consistency) is deposited.

Example 4 0.15% by weight, based on the weight of fiber, of a homopolymer of N-vinyl-Z-pyrrolidinone having a K value of 30 is incorporated into a 3.5 consistency unbleached sulfite pulp adjusted to a pH of 4.0 by addition of sulfuric acid. When tested with the vibrating plate and agitator, no pitch deposits whereas under similar test conditions the incorporation of 0.15%, on fiber, of the sodium salt of sulfonated formaldehyde/naphthalene condensate results in the deposit of 5.3 parts of pitch per 1,000 parts of pulp and 8.0 parts of pitch is deposited per 1,000 parts of pulp under similar test conditions when no addition of a pitch control agent is made.

Reduction of pitch deposition in a paper mill operation was found practically effective even when the amount of the polymer was reduced to about 0.01 to 0.04% on the fiber weight.

Example 5 0.2% by weight of a homopolymer of N-vinyl-pyrrolidinone is introduced into an unbleached sulfite pulp having a pH of 7.0. The percentage of polymer is based on the weight of fiber solids and the consistency of the pulp is 3.5% by weight of fiber. The polymer has a K value of 30 and the 5% solution in water at 25 C. shows a viscosity of 4 cps. determined in a Brookficld viscometer at 60 rpm. The equipment employed in producing paper from this composition shows greatly reduced deposition of pitch as compared with the equipment when paper is produced without the incorporation of the polymer in the pulp. Similarly, the paper sheets show very few pitch spots of minute size when obtained with the pulp containing the polymer, whereas paper sheets obtained from the pulp without the addition of polymer have relatively numerous pitch spots ranging in size from one-fourth of a millimeter to aslarge as one millimeter in average diameter. Comparative testing of the pulp with and without the 0.2% of polymer on fiber shows a pitch deposit of 0.6 part of pitch per 1,000 parts of pulp in the case or" the treated pulp and 6.9 parts of pitch per 1,000 parts of pulp in the case of the untreated pulp.

Example 6 An unbleached sulfite pulp of 3.2% consistency and having a pH of 6.7 to 8 is used for producing paper sheets. A portion of this pulp is modified by introducing into the beater 0.1% by weight, on the weight of pulp solids, of poly(N-vinyl-2-pyrrolidinone) having a K value of 60. Another portion of the pulp is used for making paper sheets without the addition of the polymer. The pitch deposition is observed at various stages during the beating with the following results. After 10 minutes of defibering (without lowering the beater roll), 0.2 part of pitch per 1,000 parts of pulp is deposited from the pulp containing the polymer, whereas 8.2 parts of pitch per 1,000 parts of pulp is deposited from the pulp which does not contain the polymer. After 30 minutes of beating, 0.7 part of pitch per 1,000 parts of pulp is deposited the polymer-containing pulp, whereas 8.9 parts of pitch per 1,000 parts of pulp are deposited in the case of the pulp which contains no added polymer.

The paper sheets obtained from the polymer-containting pulp show fewer pitch spots which have much smaller average diameters than the sheets obtained with the untreated pulp.

We claim:

1. A paper-making composition comprising fibers from a sulfite wood pulp having a content of pitch such as to give rise normally to a pitch problem by virtue of the tendency of the pitch to agglomerate and deposit in the form of particles of considerable size when umnodified by a pitch-controlling agent, the fibers in the composition consisting exclusively of cellu ose fibers, the composition having a consistency from 0.01 to 6% and containing, as a pitch-controlling material, 0.005 to 0.2% by weight, based on fiber weight, of a polymer of 80 to 100% by Weight of N-vinyl-2-pyrrolidinone.

2. A composition as defined in claim 1 in which the polymer is a copolymer containing up to 20% by weight of an ester of an acid of the formula in which n is an integer having a value of 1 to 2.

3. A composition as defined in claim 1 in which the polymer is a copolymer containing up to 20% by weight of ethyl acrylate.

4. A composition as defined in claim 1 in which the polymer is a copolymer containing up to 20% by weight of lauryl methacrylate.

5. A composition as defined in claim 1 in which the polymer is a copolymer containing up to 20% by weight of isobornyl methacrylate.

'6. The method of controlling pitch in making paper from fibers consisting exclusively of the cellulose fibers of a sulfite pulp having a pitch problem which comprises incorporating into the sulfite pulp from 0.005% to 0.2% by weight, based on the weight of the pump solids, of a polymer of to by weight of N-vinyl-Z-pyrrolidinone and up to 20% by weight of an ester of an acid of the formula CH2=C (CH2) n-iH in which n is an integer having a value of 1 to 2, at a stage between the time immediately before digestion and immediately before the time of deposition of the pump as a paper sheet, and forming a paper sheet from the pulp containing the polymer.

7. The method of controlling pitch in making paper trom fibers consisting exclusively of the cellulose fibers of a sulfite pulp having a pitch problem which comprises incorporating into the sulfite pulp from 0.005% to 0.2% by weight, based on the Weight of the pulp solids, of a homopolym'er oi Nvinyl-2-pyrrolidinone, at a stage between the time immediately before digestion and immediately before the time of deposition of the pulp as a paper sheet, and forming a paper sheet from the pulp containing the polymer.

References Cited in the file of this patent UNITED STATES PATENTS 2,335,454 Schuster Nov. 30, 1943 2,667,473 Morner Jan. 26, 1954 2,771,362 Moser Nov. 20, 1956 2,901,390 Conklin Aug. 25, 1959 2,945,863 Buc July 19, 1960 

1. A PAPER-MAKING COMPOSITION COMPRISING FIBERS FROM A SULFITE WOOD PLUS HAVING A CONTENT OF PITCH SUCH AS TO GIVE RISE NORMALLY TO A PITCH PROBLEM BY VIRTUE OF THE TENDENCY OF THE PITCH TO AGGLOMERATE AND DEPOSIT IN THE FORM OF PARTICLES OF CONSIDERABLE SIZE WHEN UNMODIFIED BY A PITCH-CONTROLLING AGENT, THE FIBER IN THE COMPOSITION CONSISTING EXCLUSIVELY OF CELLULOSE FIBERS, THE COMPOSITION HAVING A CONSISTENCY FROM 0.01 TO 6% AND CONTAINING AS A PITCH-CONTROLLING MATERIAL,, 0.005 TO 0.2% BY WEIGHT BASED ON FIBER WEIGHT, OF A POLYMER OF 80 TO 100% BY WEIGHT OF N-VINYL-2-PYRROLIDINONE. 